Apolipoprotein E (apoE) is a 299 amino acid protein present in VLDL, IDL and HDL that plays a major role in the metabolism of plasma lipoproteins. ApoE is a major ligand for the LDL and remnant receptors and thus, necessary for the normal clearance of remnant particles from the circulation. Patients with a functional deficiency of apoE can develop Type III hyperlipoproteinemia and premature atherosclerosis. We have replaced the apoE gene in apoE deficient mice with marked hypercholesterolemia and spontaneous atherosclerosis by using recombinant adenovirus expressing the human apoE gene (rapoE-AdV). Infusion of 1 X 10 9 pfu in 4 month old apoE deficient male mice (n=15) with pre-treatment TC-644+49 mg/dl and cholesterol-rich VLDL/IDL by FPLC resulted in expression of plasma apoE concentrations ranging from 3 to 650 mg/dl and normalization of the plasma lipids and lipoproteins by day 4 post-virus injection. ApoE expression and normal reduced plasma lipids were maintained for a period of 4 weeks after virus injection. Analysis of aortic lesions in apoE deficient mice injected with rapoE-AdV demonstrated a marked reduction in the mean lesion area (58+/-35 X 10 3 mu m2)compared to untreated mice (135+/-71 x 10 mu m2) and animals injected with rLuciferase-AdV(161+/-73 X 10 3mu m2). Our studies demonstrate successful replacement of human apoE in apoE deficient mice using recombinant adenovirus. Expression of physiologic concentrations of apoE for 1 month normalized plasma lipids and lipoproteins and resulted in marked reduction in mean aortic lesion area. Successful replacement of apoE in apoE deficient mice demonstrates the feasibility of gene therapy for human genetic apolipoprotein deficiencies.